While I like a lot of the functional features touted, purescript is effectively a new language. This drops the familiarity advantage, which I see as one of the main reasons for using JavaScript over other options. I think https://www.typescriptlang.org/ is striking a more user friendly compromise here, by adding lightweight typing, but still retaining familiarity to JS engineers.

If on the other hand we were willing to entertain completely new languages, then there might be better choices than purescript. With webassembly, more languages are set to become efficiently compilable to the web. Among other things, this includes modern C++ and (of course I had to mention it..) Rust.